Viruses have been the cause of some of the greatest epidemics in human history including smallpox and AIDS. Although viruses must circumvent the host immune response in order to establish infection, the viral factors and mechanisms by which this occurs are largely unknown. Insights into these viral strategies can be harnessed by understanding the evolutionary dynamics of host genes. I am utilizing the cGAS/STING pathway, which serves as a first responder in poxvirus, herpesvirus, and HIV-1 infections, as a model to uncover the strategies used by viruses and host immunity to counteract each other. Upon binding viral DNA, cGAS generates the second messenger cGAMP, which activates a signaling cascade via STING leading to interferon expression. In this proposal, I aim to build off of my previous postdoctoral work in which I used evolutionary and phylogenetic principles to characterize recurrent cGAS adaptation in response to selection imposed by pathogens. During the K99 mentored phase I will be investigating the role of cGAS spliceforms that I identified in the evasion of viral-mediated inhibition and regulation of host immunity. In contrast, I am also focusing on the first viral factor directly implicated in the inactivation of cGAS signaling, whichI discovered, and its role in viral replication. Further building on my initial work on cGAS, I am using signatures of positive selection to identify new immunity factors. To date, I have several candidate genes which are rapidly evolving in a manner similar to other critical immunity factors such as Protein Kinase R and APOBEC3G. In addition to my work investigating the cGAS-viral interface, these rapidly evolving genes will serve as a platform during the R00 phase to launch my independent research program. Combining my past training in human genetics with Dr. Haig Kazazian Jr. and evolutionary biology with Dr. Nels Elde with my new training in virology facilitated by this K99 award, I will be able to address diverse biological problems. My research program aims to not only aid in treating viral disease but genetic disorders like lupus. Moreover, my laboratory will be an integrated reflection of my academic experiences at Southern Illinois University, University of Pennsylvania, Johns Hopkins, and University of Utah. To date my success over the years can be attributed to the fine mentors and opportunities I have been provided. Thus, to drive and enrich my research program, I will continue to seek out mentoring opportunities as I have over the years. I will continue this tradition by running a multi-disciplinry and collaborative lab by providing frequent informal and formal opportunities to discuss science and by recruiting trainees from multiple graduate programs with emphasis on making fundamental discoveries using evolution- guided approaches in basic science and virology.